Why Are There No Interior Points in the Set of Real Numbers?

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Discussion Overview

The discussion revolves around the concept of interior points in the set of rational numbers (Q) and its complement in the real numbers (R\Q). Participants explore why these sets are said to lack interior points, engaging with definitions and implications of neighborhoods in the context of real analysis.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Omri questions the assertion that the set Q has no interior points and seeks clarification on the concept.
  • One participant proposes that for a rational number q to be an interior point of Q, there must exist a neighborhood around q that contains only rational numbers.
  • Another participant points out that one can place a real number between any two rational numbers, suggesting a potential misunderstanding about the nature of interior points.
  • A subsequent reply corrects the previous statement, indicating that the relevant discussion should focus on irrational numbers rather than real numbers in general.
  • Clarification is provided that for a point to be an interior point of R\Q, there must exist an interval around that point consisting entirely of irrational numbers, which is also not possible.
  • Omri reiterates the statement regarding the lack of interior points in both Q and R\Q, confirming the group's understanding of the topic.

Areas of Agreement / Disagreement

Participants generally agree on the assertion that both Q and its complement R\Q lack interior points, although some nuances and misunderstandings about the definitions and implications are present in the discussion.

Contextual Notes

There are unresolved aspects regarding the definitions of neighborhoods and the implications of having intervals consisting entirely of rational or irrational numbers. The discussion reflects varying levels of understanding among participants.

omri3012
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Hallo,

My teacher wrote that:

"The set has no interior points, and neither does its complement, R\Q" where R refers real

numbers and Q is the rationals numbers.

why can't i find an iterior point?

thanks,

Omri
 
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Let q be an arbitrary rational number. Does there exist a neighborhood of q that is a subset of Q?
 
How about the fact that I can squeeze a real number between any two arbitrary points of Q?
 
trambolin said:
How about the fact that I can squeeze a real number between any two arbitrary points of Q?
Irrelevant. Do you mean an irrational number? Now that would be relevant.
 
omri3012 said:
Hallo,

My teacher wrote that:

"The set has no interior points, and neither does its complement, R\Q" where R refers real

numbers and Q is the rationals numbers.

why can't i find an iterior point?

thanks,

Omri
So "the set" is Q. For p to be an interior point of Q, there must exist an interval around p, [math](p-\delta, p+\delta)[/quote] consisting entirely of rational numbers. For p to be an interior point of R\Q, the set of irrational numbers, there must exist an interval [itex](p- \delta, p+ \delta)[/itex]] consisting entirely of irrational numbers. There is NO interval of real numbers consisting entirely of rational number or entirely of irrational numbers.
 
Last edited by a moderator:
That was what I said anyway, but of course a real is not necessarily rational part got lost along the way... Sorry for that.
 
thank you for your comments,

I'm sorry but the statement (as i guess you already assume) was:

"The set Q has no interior points, and neither does its complement, R\Q"

thanks

Omri
 
Yes, that was essentially what everyone was assuming.
 

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